1. Field of the Invention
The present invention relates to a semiconductor device. Note that in this specification, a semiconductor device refers to a device including a semiconductor element. As such a semiconductor element, a transistor is given, for example. Further, the semiconductor device includes a liquid crystal display device and the like.
2. Description of the Related Art
In contrast to transistors manufactured using silicon, attention has been drawn to a technique by which a transistor is manufactured using an oxide semiconductor, which is a wide-gap semiconductor, for its channel and is applied to an electronic device or an optical device. For example, a technique of manufacturing a transistor by using zinc oxide or In—Ga—Zn—O-based oxide as an oxide semiconductor, and using the transistor for a switching element of a pixel of a display device and the like is disclosed in Patent Document 1 and Patent Document 2.